The present invention relates to a process control system.
FIG. 1 illustrates a process control system in which a process is implemented by a process model or individual process submodels. For example, the process may include the filling of a combustion chamber of an internal combustion engine with a desired mixture of air and gas. Based on a desired filling specified by the driver, the desired manipulating variables for driving individual load actuators are determined by a first process model component PM1, for example, in the form of a load control.
The actual filling of the combustion chamber is calculated by a second process model PM2 in the form of a load determination, which is based on the process-determined actual manipulating variables of the load actuators. Parallel to the calculation of this actual filling, the actual filling is measured via sensors, for example, an HFM sensor. The measured and the calculated actual filling are then compared. The difference between the actual fillings is fed to a mass flow regulator, which in turn influences the two process models via its output signal. Since one model must be invertible for observing a process, the process models PM1 and PM2 must be invertible. Thus, PM1 must be invertible into PM2 and vice versa. To guarantee this invertability at any time, only such process models are employed that are very simplified and, therefore, usually also very inaccurate.
The present invention provides a solution to the above-described problem by providing a process control system exhibiting higher precision.
A process control system according to the invention includes a first process model for driving at least one process actuator in such a manner that, from at least one process desired variable fed to the first process model, at least one process desired manipulating variable is generated for driving at least one process actuator. Furthermore, there is a second process model, which generates a process actual variable from at least one process actual manipulating variable of the at least one process actuator. Therefore, the first process model can be mapped (transferred into the second process model) by inverting the second process model. Furthermore, according to the invention, a third process model generates a comparison process actual variable, which is substantially equivalent to the process actual variable generated by the second process model. The third process model may have a distinctly higher precision and exhibit at least one non-invertible component in such a manner that the third process model cannot be converted in its entirety through inversion into the first process model. Furthermore, a process actual variable difference may be formed from the process actual variable and the comparison process actual variable. The difference is fed via a first control unit back to the first and the second process models.
In an exemplary embodiment of the invention, there is a device for measuring a comparison process actual variable. In so doing, an additional process actual variable difference, formed from the measured comparison process actual variable and the process actual variable and determined via the third process model, is fed via another control unit back to the third process model.
An exemplary embodiment of the invention includes determining the load and controlling the load for the combustion engine of a motor vehicle.
The exact knowledge of the air mass flowing into the combustion chambers of the cylinders per working cycle, which is also called the load, is very important for controlling internal combustion engines. The calculation of the injection period for the fuel and the calculation of the ignition point for the mixture of air and fuel in the combustion chamber are carried out based on the load. When regulating and/or controlling the process, any inaccuracies in the load signal usually result in a disadvantageous behavior of the emissions, drivability and consumption.
A direct determination of the air mass flow at the intake valve, which is mandatory for controlling and/or regulating the process, is not possible for technical reasons. Thus, accurate models for calculating the air mass flow ratios at the intake valve are necessary for controlling and/or regulating internal combustion engines. This is done, for example, on the basis of pressure sensors, mass flow sensors at the intake to the suction system (e.g., HFM sensors) or with the aid of actual variables of the actuators (e.g., throttle flap). This model-based calculation of the load is called load determination. In addition to the load determination, a load control may be implemented in the control of the internal combustion engine. To this end, the load setpoint, which is the result of the driver's momentary wish, is converted into the setpoints for the load actuators. In an engine with adjustable valve lift and/or adjustable valve timing (e.g., a Valvetronic engine), the suitable load setpoints to be calculated (load determination) are the following variables: throttle flap setting, intake valve lift, exhaust valve lift, intake timing, and exhaust timing.
Even for load control, the calculation models, in which the connection between the load and the positions or the values of the load actuators are mapped, must be put in the control/regulation. A fundamental difference between the two control functions (load control and load determination) to be reproduced by process models lies in the demands put on the respective air mass models. On the one hand, the process model that is used for load determination ought to map the process to be reproduced as accurately as possible. Since an invertability is not absolutely necessary for load determination, yet higher accuracy is desired, a process model that is not invertible in its entirety is used to this end. Therefore, a first process model for load determination is designed so as to be invertible in order to infer by inversion the process model for the precontrol (load control). A second process model for load determination is designed to be non-invertible to achieve higher accuracy for the load determination, if necessary.
On the other hand, the process model used for load control ought to be invertible, because the actuation of the load actuators must be based on the inverted air mass model. The use of an inverted or invertible process model in the precontrol (load control) guarantees that at stationary operating points the load setpoints and the load actual values are equal, and thus, the functioning of the so-called torque structure of the control is guaranteed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.